ABS resins are characterized by the balanced properties such as impact resistance, mechanical strength, moulding processability and a surface gloss so that they are widely used as parts of an automobile, electric and electronic appliances, office automated machines and electric home appliances. ABS resins having a high gloss are especially applied to parts requiring an excellent surface gloss.
Gloss of an ABS resin depends on rubber content, size and distribution of rubber particles. Rubbers having a small particle diameter have a high gloss while they have low impact resistance and low melt flow rate. Accordingly, in order to prepare thermoplastic resins having a high gloss and excellent impact resistance, it is necessary to mix rubber latices having a small particle diameter and rubber latices having a large particle diameter, appropriately.
Japanese Patent Publication No. (Sho)60/250057 described a process for preparing a thermoplastic resin after agglomeration the rubber latex having a small particle diameter in accordance with an agglomeration method using the shearing force of a homogenizer. However, according to this process, non-agglomerated particles having a small particle diameter are still remained due to the character of an agglomeration method using a homogenizer. Thus, if the rubber latex having a small particle diameter is used alone, the impact strength and the melt flow rate are lowered. Therefore, in order to solve these problems, the present invention has used a rubber latex having a large particle diameter (hereinafter referred to as "large-diameter latex") of 0.25.about.0.4.mu. in combination with a rubber latex having a small particle diameter (hereinafter referred to as "small-diameter latex") while its gloss is maintained, and the impact strength and the melt flow rate are improved.
As a general agglomeration method, it is well known that dispersions of the rubber latices can be agglomerated by using acids, salts, freezing, solvents, high molecular weight agglomerating agents and high shear force (pressure agglomeration). Such an agglomeration method has its own characteristic. If a pressure agglomeration method is used, non-agglomerated rubber particles of at least 38% exist. Furthermore, if an acid agglomeration method is used, the rubber having a monodisperse distribution which has a narrow distribution, may be obtained.
Thus, the present inventors have controlled the distribution of particle diameter of whole rubber particles in order to obtain a high gloss due to the non-agglomerated rubber particles having a small particle diameter by a pressure agglomeration method and impact resistance due to the agglomerated rubber particles having a large particle diameter by an acid agglomeration method.